There is a vehicle seat including, what is called, a walk-in mechanism. In addition to an operation for changing angle of a seat back, the walk-in mechanism enables to release a lock of the seat back to instantaneously make a seat back fall forward, for example, when an occupant moves to a back seat by opening a front side door in a two door typed coupe.
As a background art in this technical field, there is Japanese Patent Application Laid-Open No. 2008-296659 (PTL 1). PTL 1 discloses a mechanism that positions the position of the center of gravity of a lock plate below an axial center position of a turning shaft in a locking device of a vehicle seat back that retains the seat back at a seating posture position by turning the lock plate about the turning shaft and engaging the lock plate with a lock pin, for the purpose of providing a locking device of a vehicle seat back that ensures further reliably retaining a lock state of the seat back at a seating posture position.